Reconfigurable multiple beam satellite reflector antenna with an array feed

ABSTRACT

A reconfigurable multiple beam array antenna for transmitting beams includes a reflector and radiating elements for feeding beam signals to the reflector. The array antenna includes a reconfigurable beam forming network having a plurality of dividers, a plurality of adjustable phase shifter and attenuator pairs, and a plurality of combiners to form beam signals from beam signals input to the beam forming network. A first hybrid matrix formed by an association of couplers is connected to the beam forming network for receiving the beam signals. Amplifiers receive and amplify the beam signals from the first hybrid matrix. A second hybrid matrix formed by an association of couplers is connected to the amplifiers for receiving the beam signals. The second hybrid matrix provides the amplified beam signals to the radiating elements for the reflector to transmit beams.

TECHNICAL FIELD

The present invention relates generally to array antennas and, moreparticularly, to reconfigurable multiple beam array antennas.

BACKGROUND ART

The advent of wireless forms of communication necessitated the need forantennas. Antennas are required by communications and radar systems, anddepending upon the specific application, antennas can be required forboth transmitting and receiving signals. Early stages of wirelesscommunications consisted of transmitting and receiving signals atfrequencies below 1 MHz which resulted in signal wavelengths greaterthan 0.3 km. A problem with such relatively large wavelengths is that ifthe size of the antenna is not at least equal to the wavelength, thenthe antenna is not capable of directional transmission or reception. Inmore modern forms of wireless communications, such as withcommunications satellites, the frequency range of transmitted signalshas shifted to the microwave spectrum where signal wavelengths are inthe 1.0 cm to 30.0 cm range. Therefore, it is practical for antennas tohave sizes much greater than the signal wavelength and achieve highlydirectional radiation beams.

Many antennas have requirements for high directivity, high angularresolution, and the ability to electronically scan or be reconfigured.These functions are typically accomplished using an array antenna. Anarray antenna includes a collection of radiating elements closelyarranged in a predetermined pattern and energized to produce beams inspecific directions. When elements are combined in an array,constructive radiation interference results in a main beam ofconcentrated radiation, while destructive radiation interference outsidethe main beam reduces stray radiation. To produce desired radiationpatterns, each individual radiating element is energized with the properphase and amplitude relative to the other elements in the array.

In satellite communications systems, signals are typically beamedbetween satellites and fixed coverage region(s) on the Earth. With theexpanding applications of satellites for many different aspects ofcommunications, market requirements are continuously changing.Accordingly, a satellite must be capable of adapting to changes in thelocation of the service requests. Thus, antennas provided on satellitemust be capable of reconfigurable coverages.

A reconfigurable multiple beam array antenna is an ideal solution to theever changing beam coverage requirements. Beam coverage can be in theform of a number of spot beams and regional beams located over specificregions. Spot beams cover discrete and separate areas such as cities.Regional beams cover larger areas such as countries. Regional beams aregenerated by combining a plurality of spot beams. Spot beams aregenerated by energizing the radiating elements with selected amplitudesand phases. A reconfigurable multiple beam array antenna should becapable of reconfiguring the location of the beams, the size of thebeams, and the power radiated in each beam.

What is needed is a reconfigurable multiple beam array antenna in whichreconfigurability is achieved by selecting radiating elements of thearray to excite for generating beams.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide areconfigurable multiple beam array antenna in which any radiatingelement can be selected for any given input beam port.

It is another object of the present invention to provide areconfigurable multiple beam array antenna which may use all theradiating elements for each beam.

It is a further object of the present invention to provide areconfigurable multiple beam array antenna which may use only oneradiating element for each beam.

It is still another object of the present invention to provide areconfigurable multiple beam array which includes a reconfigurable beamforming network having dividers, phase shifter and attenuator pairs, andcombiners.

In carrying out the above objects and other objects, the presentinvention provides a reconfigurable multiple beam array antenna fortransmitting beams. The array antenna includes a reflector and aplurality of radiating elements arranged in either a planar or aspherical surface for feeding beam signals to the reflector. The arrayantenna further includes a reconfigurable beam forming network having aplurality of dividers, a plurality of adjustable phase shifter andattenuator pairs, and a plurality of combiners to form beam signals frombeam signals input to the beam forming network. A first hybrid matrixformed by an association of couplers is connected to the beam formingnetwork for receiving the beam signals from the beam forming network. Aplurality of amplifiers receives and amplifies the beam signals from thefirst hybrid matrix. A second hybrid matrix formed by an association ofcouplers is connected to the plurality of amplifiers for receiving thebeam signals from the plurality of amplifiers. The second hybrid matrixprovides the amplified beam signals to the plurality of radiatingelements for the reflector to transmit beams.

In accordance with the array antenna for transmitting beams, areconfigurable multiple beam array antenna for receiving beams is alsoprovided.

The advantages accruing to the present invention are numerous. Multiplebeams with widely shaped coverages can be generated unlike theconventional approaches which generate uniform sized spot beams. Thereflector of the array antenna can be gimballed to scan the beams over awide-angular area using only a relatively small feed array and low orderhybrid matrices. Further, the array antenna can be easily reconfiguredto compensate for on orbit failures of the amplifiers and, thus,requires a relatively small number of redundancies. Compensation can beachieved by using a different set of beam forming network output portexcitations which will optimize the given beam shapes taking intoaccount the failure of a particular amplifier.

These and other features, aspects, and embodiments of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a reconfigurable multiple beam arrayantenna according to a first embodiment of the present invention fortransmitting beams;

FIG. 2 is a block diagram of the beam forming network of the arrayantenna shown in FIG. 1;

FIG. 3 is a block diagram of the pair of hybrid matrices and amplifiersof the array antenna shown in FIG. 1;

FIG. 4 is a block diagram of a reconfigurable multiple beam arrayantenna according to a second embodiment of the present invention forreceiving beams;

FIG. 5 is a block diagram of a reconfigurable multiple beam arrayantenna according to a third embodiment of the present invention fortransmitting beams; and

FIG. 6 is a block diagram of a reconfigurable multiple beam arrayantenna according to a fourth embodiment of the present invention fortransmitting beams.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, a reconfigurable multiple beam array antenna 10according to a first embodiment of the present invention is shown. Arrayantenna 10 is operable for transmitting beams and is intended for use ona satellite (not specifically shown in FIG. 1). Array antenna 10includes right and left hand circular polarization antenna subsystems12a and 12b connected to N radiating elements 14(a-n) by respectivepolarizers 16(a-n) along separate individual feed chains 18(a-n).Radiating elements 14(a-n) are arranged in either a planar surface forsmall coverages or along a spherical surface for large coverages andfeed a reflector 20. Of course, radiating elements may feed asubreflector which then feeds reflector 20. Radiating elements 14(a-n)can be located close to the focal plane of reflector 20 or over a planewhich can be defocused from the focal plane. Preferably, radiatingelements 14(a-n) are defocused and located several wavelengths away fromthe focal plane of reflector 20 in order to provide betterreconfigurability of the beams. Because antenna subsystems 12a and 12binclude the same elements, only antenna subsystem 12a will be describedin further detail.

Antenna subsystem 12a includes a pair of N×N hybrid matrices 22 and 24connected back to back by N amplifiers 26(a-n). Amplifiers 26(a-n) aredistributed non-redundant traveling wave tube amplifiers (TWTA) or solidstate power amplifiers (SSPA). Output hybrid matrix (OHM) 22 includes NOHM output ports 28(a-n) and N OHM input ports 30(a-n). Each one of OHMoutput ports 28(a-n) is connected to a respective one of radiatingelements 14(a-n) along respective individual feed chains 18(a-n). Eachone of OHM input ports 30(a-n) is connected to the output of arespective one of amplifiers 26(a-n). Input hybrid matrix (IHM) 24includes N IHM output ports 32(a-n) and N IHM input ports 34(a-n). Eachone of IHM output ports 32(a-n) is connected to the input of arespective one of amplifiers 26(a-n). (The redundancy schematic foramplifiers 26(a-n) is not shown in FIG. 1.)

Antenna subsystem 12a further includes a reconfigurable beam formingnetwork (BFN) 36. BFN 36 includes N BFN output ports 38(a-n) and I BFNbeam input ports 40(a-i). Each one of BFN output ports 38(a-n) isconnected to a respective one of IHM input ports 34(a-n).

Referring now to FIG. 2 with continual reference to FIG. 1, a blockdiagram of BFN 36 is shown. BFN 36 excites any specified number of BFNoutput ports 38(a-n) by processing signals input to the BFN from BFNbeam input ports 40(a-i). Hence, radiating elements 14(a-n)corresponding to BFN output ports 38(a-n) are also excited (as discussedbelow) to form beams. Thus, beams with different locations, sizes, andpower levels can be generated by reconfiguring BFN output ports 38(a-n)for each one of BFN beam input ports 40(a-i).

BFN 36 includes I (1:N) dividers 46(a-i), N (I:1) combiners 50(a-n), andI variable phase shifter and attenuator pairs 48(a-i) associated witheach of the N combiners. Dividers 46(a-i) divide each one of the I beamsignals from BFN beam input ports 40(a-i) into N beam signals.

Each one of the divided N beam signals from dividers 46(a-i) is routedto a phase shifter and attenuator pair 48(a-i). For instance, the firstdivided beam signal from divider 46a is routed to the first phaseshifter and attenuator pair 48a associated with combiner 50a. Similarly,the second divided beam signal from divider 46a is routed to first phaseshifter and attenuator pair 48a associated with combiner 50b. The Nthdivided beam signal from divider 46a is routed to the first phaseshifter and attenuator pair 48a associated with the Nth combiner 50n.

This routing pattern is followed for each of the other dividers 46(b-i).For instance, the first divided beam signal from divider 46b is routedto the second phase shifter and attenuator pair 48b associated withcombiner 50a. Similarly, the second divided beam signal from divider 46bis routed to second phase shifter and attenuator pair 48b associatedwith combiner 50b. The Nth divided beam signal from divider 46i isrouted to the Ith phase shifter and attenuator pair 48i associated withthe Nth combiner 50n.

Phase shifter and attenuator pairs 48(a-i) vary the phase and amplitudeof each of the divided N beam signals from dividers 46(a-i). Phaseshifter and attenuator pairs 48(a-i) are active components used to formthe beams. Phase shifter and attenuator pairs 48(a-i) output the phaseshifted and amplitude adjusted I divided beam signals to theirassociated combiners 50(a-n). Each of combiners 50(a-n) combines the Idivided beam signals from their associated phase shifter and attenuatorpairs 48(a-i) into a combined beam signal. The combined beam signalsfrom combiners 50(a-n) are output on respective ones of BFN output ports38(a-n). A pair of N×I variable phase shifter and attenuator pairs arerequired to provide the complete reconfigurability.

Referring now to FIG. 3 with continual reference to FIG. 1, the combinedbeam signals from combiners 50(a-n) are input from BFN output ports38(a-n) to IHM 24 via respective IHM input ports 34(a-n). In general,IHM 24 and OHM 22 generate the image of each one of IHM input ports34(a-n) on the corresponding OHM output port 28(a-n) and so excite aparticular one of radiating elements 14(a-n). Thus, a number ofradiating elements 14(a-n) can be excited by selecting the correspondingnumber of IHM input ports 34(a-n) (or BFN output ports 38(a-n)).

IHM 24 equally divides the combined beam signal on each one of IHM inputports 34(a-n) into N divided signals having a systematic phasedifference. The N divided signals are then output onto corresponding IHMoutput ports 32(a-n). The N divided signals from IHM output ports32(a-n) are amplified by respective ones of N amplifiers 26(a-n) andthen input to OHM 22 via OHM input ports 30(a-n). OHM 22 combines theamplified N divided signals from OHM input ports 30(a-n) systematicallyto remove the phase differences between the signals and then outputs thecombined signals onto corresponding OHM output ports 28(a-n). Thecombined signals from OHM output ports 28(a-n) are then fed to radiatingelements 14(a-n) along respective feed chains 18(a-n).

Radiating elements 14(a-n) then feed reflector 20 for the reflector totransmit beams. A gimballing mechanism 56 is operable with reflector 20to rotate and tilt the reflector. The rotation and tilting of reflector20 enables the transmitted beams to be steered to obtain globalreconfigurability.

Because each one of OHM output ports 28(a-n) is connected to arespective one of radiating elements 14(a-n), each one of IHM inputports 34(a-n) and BFN output ports 38(a-n) corresponds to a specificradiating element. Thus, BFN 36 allows any specific number of radiatingelements 14(a-n) to be selected to form a beam for a given one of BFNbeam input ports 40(a-i). Multiple beams can be formed by associatingdifferent combinations of radiating elements 14(a-n) to BFN beam inputports 40(a-i). By varying the input power levels to BFN beam input ports40(a-i), the power associated with different beams can also becontrolled.

The amplified signals on OHM output ports 28(a-n) were amplified usingthe power from all of amplifiers 26(a-n). This is highly advantageousbecause it is difficult to sum beams of different phases and amplitudeswithout giving rise to losses. If summing is performed prior toamplification to obtain the generated beams, amplifiers 26(a-n) will beloaded differently and as a result it is no longer possible to obtainlinear amplification or constant gain.

In order to load amplifiers 26(a-n) uniformly, IHM 24 and OHM 22 areused to get as close as possible to optimum operating conditions witheach one of amplifier 26(a-n) providing optimum efficiency while workingat optimum operating points. IHM 24 includes 3 dB couplers 52 arrangedsuch that the combined beam signal on each one of IHM input ports34(a-n) is equally divided into N divided signals having a systematicphase difference. This gives rise to a uniform load distribution overall of the inputs of amplifiers 26(a-n).

OHM 22 includes 3 dB couplers 54 arranged to combine the amplified Ndivided signals systematically to remove the phase differences betweenthe signals. Thus, the original signals from BFN output ports 38(a-n)are recovered after amplification. The arrangement of 3 dB couplers 54of OHM 22 is inverse to the arrangement of 3 dB couplers 52 of IHM 24.

Referring now to FIG. 4, a reconfigurable multiple beam array antenna 60(for single polarization) according to a second embodiment of thepresent invention is shown. Array antenna 60 is operable for receivingbeams and is intended for use on a satellite (not specifically shown inFIG. 4). Array antenna 60 generally includes the same elements as arrayantenna 10 shown in FIG. 1. Array antenna 60 differs from array antenna10 by including N low noise amplifiers (LNA) 62(a-n) connected betweenthe pair of hybrid matrices 22 and 24.

For array antenna 60 to operate in the receive mode, the above describedprocedure of array antenna 10 is reversed. For instance, OHM 22 performsthe function of IHM 24 and the IHM performs the function of the OHM tosupply signals to BFN 36. In BFN 36, referring briefly to FIG. 2, eachone of combiners 50(a-n) functions to divide the supplied signal into Isignals. The I divided signals from each one of combiners 50(a-n) arethen provided to phase shifter and attenuator pairs 48(a-i) associatedwith the respective combiners. Phase shifter and attenuator pairs48(a-i) adjust the phase and amplitude of the signals and then route thesignals to associated dividers 46(a-i). Each one of dividers 46(a-i)receives N signals and combines the N signals into one signal. Thecombined signals are then provided onto BFN beam input ports 40(a-i) forprocessing.

Referring now to FIG. 5, a reconfigurable multiple beam array antenna 70according to a third embodiment of the present invention is shown. Arrayantenna 70 is operable for transmitting beams and is intended for use ona satellite (not specifically shown in FIG. 5). Array antenna 70generally includes the same elements as shown in FIG. 1 for arrayantenna 10. Array antenna 70 differs from array antenna 10 by replacingOHM 22 and IHM 24 with a group of M×M hybrid matrices 72(a-c) and74(a-c). The N and M orders are related by the equation N=cM where c isthe number of hybrid matrices 72(a-c) and 74(a-c). Using smaller orderedmatrices is desirable with applications involving large values of N inwhich an N×N matrix is too complex to build.

Referring now to FIG. 6, a reconfigurable multiple beam array antenna 80according to a fourth embodiment of the present invention is shown.Array antenna 80 is operable for transmitting beams and is intended foruse on a satellite (not specifically shown in FIG. 6). Array antenna 80generally includes the same elements as shown in FIG. 1 for arrayantenna 10. Array antenna 80 differs from array antenna 10 by includinga L×N switch 82. Switch 82 allows BFN 36 to be simpler to operate byoperating on a subset of radiating elements 14(a-n) instead of operatingon all the radiating elements.

A smaller subset (up to L) of radiating elements 14(a-n) can be selectedby switch 82 thus forming beams over a smaller region of the Earth. Byselecting different subsets, beams can be formed in different parts ofthe Earth. In this configuration, radiating elements 14(a-n) and OHM 22and IHM 24 are designed for a larger coverage region but BFN 36 isdesigned for a smaller coverage region.

The present invention is applicable to satellite based communications.It is particularly of interest to future communications satellites suchas personal communications satellites (PCS), direct broadcast satellites(DBS), and mobile communications satellites involving a moderate tolarge number of multiple beams.

Thus it is apparent that there has been provided, in accordance with thepresent invention, a reconfigurable multiple beam array antenna thatfully satisfies the objects, aims, and advantages set forth above.

The present invention allows a single antenna to be used for a widevariety of customer requirements, resulting in a generic antenna designwith an associated reduction of cost and schedule. As an example, thesame antenna design can be used for a large country such as the UnitedStates or a small country such as Greece. This may lead to multiplesatellites to be manufactured with the option of customizing prior tolaunch or even on-orbit. The satellites can be moved from one orbit toanother with minimum performance degradation. The reconfigurabilityreduces the burden on determining marketing needs.

While the present invention has been described in conjunction withspecific embodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedto embrace all such alternatives, modifications, and variations as fallwithin the spirit and broad scope of the appended claims.

What is claimed is:
 1. A reconfigurable multiple beam array antenna fortransmitting beams comprising:a reflector; a plurality of radiatingelements for feeding beam signals to the reflector; a reconfigurablebeam forming network, the beam forming network including a plurality ofdividers, a plurality of adjustable phase shifters and attenuator pairs,and a plurality of combiners to form beam signals from beam signalsinput to the beam forming network; a first hybrid matrix formed by anassociation of couplers connected to the beam forming network forreceiving the beam signals from the beam forming network; a plurality ofamplifiers for receiving and amplifying the beam signals from the firsthybrid matrix; and a second hybrid matrix formed by an association ofcouplers connected to the plurality of amplifiers for receiving the beamsignals from the plurality of amplifiers, wherein the second hybridmatrix provides the amplified beam signals to the plurality of radiatingelements for the reflector to transmit beams.
 2. The array antenna ofclaim 1 wherein:the plurality of radiating elements are located on thefocal plane of the reflector.
 3. The array antenna of claim 1wherein:the plurality of radiating elements are located over a planewhich is defocused from the focal plane of the reflector.
 4. The arrayantenna of claim 1 wherein:the couplers of the first and second hybridmatrices are 3 dB couplers.
 5. The array antenna of claim 1 wherein:theplurality of amplifiers are traveling wave tube amplifiers.
 6. The arrayantenna of claim 1 wherein:the plurality of amplifiers are solid statepower amplifiers.
 7. The array antenna of claim 1 wherein:the pluralityof dividers divide each one of the beam signals input to the beamforming network into divided beam signals and then routes the dividedbeam signals to the phase shifters and attenuator pairs.
 8. The arrayantenna of claim 7 wherein:the phase shifters and attenuator pairsadjust the phase and amplitude of the divided beam signals and thenprovide the adjusted divided beam signals to the combiners.
 9. The arrayantenna of claim 8 wherein:the combiners combine the adjusted dividedbeam signals into the output beam signals.
 10. The array antenna ofclaim 1 wherein:the first and second hybrid matrices include a pluralityof hybrid matrices.
 11. The array antenna of claim 1 furthercomprising:a switch which connects the beam forming network to the firsthybrid matrix.
 12. The array antenna of claim 1 further comprising:agimballing mechanism for tilting and rotating the reflector to steer thetransmitted beams.
 13. A reconfigurable multiple beam array antenna forreceiving beams comprising:a reflector; a plurality of radiatingelements for receiving beam signals from the reflector; a first hybridmatrix formed by an association of couplers connected to the pluralityof radiating elements for receiving the beam signals from the pluralityof radiating elements; a plurality of amplifiers for receiving andamplifying the beam signals from the first hybrid matrix; a secondhybrid matrix formed by an association of couplers connected to theplurality of amplifiers for receiving the amplified beam signals fromthe plurality of amplifiers; and a reconfigurable beam forming network,the beam forming network including a plurality of dividers, a pluralityof adjustable phase shifters and attenuator pairs, and a plurality ofcombiners to form beam signals from the amplified beam signals input tothe beam forming network from the second hybrid matrix.
 14. The arrayantenna of claim 13 wherein:the plurality of amplifiers are low noiseamplifiers.